There are known gear pumps for hydraulic systems which are equipped with two gears. The gear cogs interlock, wherein during rotation they carry the working fluid from the suction space into the discharge space, and they are simultaneously in tight contact with each other to prevent the return of the working fluid from the discharge space into the suction space. The gears, together with the sleeves of the pins, are stored in the pump housing, wherein one of the gears is driven and the second gear is driving. The drive gear is connected with a drive via a shaft extending through the housing, which is rigidly attached to the housing of the gear pump by a flange. Waste heat is removed from the drive by an integrated cooling circuit. Gear pumps are widely used in a variety of technical fields, including aviation, where they are used e.g. for refueling aircraft turbine engines, for example of Auxiliary Power Units (APU) which serve to power aircraft electrical systems and starting systems. Such gear pumps have high demands on smooth operation and stability of performance and traffic parameters.
The disadvantages of gear pumps consist in the fact that during pump operation at a high working fluid pressure, a loss flow occurs between the moving and the stationary parts of the pump. It is also necessary to ensure good lubrication of the contact surfaces of the movable and stationary parts, since the gears operate at high rotational speeds. High rotational speeds also cause the release of heat within the housing of the gear pump, which heats up. Overheating the housing leads to volume changes in the material, which may lead to malfunction or instability of the operating parameters. The drive which is connected to the housing of the gear pump also heats up and requires lubrication and cooling in the areas of friction of the moving and stationary parts. Loss flow is formed by the working fluid, which, influenced by high pressure, is pushed between the moving and the stationary parts of the gear pump, for example between the gear pins and their sleeves.
The problem with the loss flow of the working fluid is resolved for example by patent document U.S. Pat. No. 4,470,776 B, which describes a gear pump whose loss flow is guided by at least one means for guiding the loss flow. The means consists of channels around the pins and bearings for their lubrication and reduction of friction, whereupon the loss flow is led back into the suction space of the pump, i.e. to the suction inlet.
The issue of cooling the drive can be resolved by an external cooling circuit which has its own cooling medium and which is equipped with its own pump and which is integrated into the drive system and the gear pump. The disadvantages of the external cooling are that it makes the drive assembly and the gear pump more complicated by design, heavier, bulkier, and more expensive. If the externally cooled gear pump with drive should be used in aviation, the large mass of the assembly is a complication and a considerable disadvantage.
Another patent document GB 1 133 737 B describes an invention in which the loss flow of the pump uses the gears of the pump to cool the shaft. This eliminates the need to externally cool the gear pump, because the working fluid replaces the cooling medium. The disadvantage of this solution is that it does not solve the cooling of the drive unit, so the drive unit must be equipped with external cooling or cooled in another way.
The task of the present invention is to create a gear pump with a drive that would eliminate the aforementioned disadvantages and which would be characterized by a simple and operationally reliable system of cooling the drive, with complete elimination of the need for external cooling circuits or devices. Such a gear pump could be deployed in the area of high pressures, with minimum size and weight, while maintaining reliability and stability of the operating parameters.